Rarobelus nom. nov. from the Boreal Toarcian-Aalenian and its systematic position (Belemnitida, Belemnitina, Megateuthididae)
Dzyuba, Oksana S.; Weis, Robert; Nalnjaeva, Tamara I.; Riegraf, Wolfgang
published: Mar 1, 2015
The belemnite genus Orthobelus Nalnjaeva, in Sachs & Nalnjaeva 1970, was revealed to be a junior homonym of the treehopper genus Orthobelus Stål, 1869 (Insecta), and it is replaced by Rarobelus Nalnjaeva nom. nov. This Early Toarcian-Early Aalenian Subarctic-Arctic genus is characterised by a marked conical shape at all stages of the ontogeny. Consequently, it does not belong to the family Passaloteuthididae Naef, 1922, as commonly supposed earlier, but is an early representative of the family Megateuthididae Sachs & Nalnjaeva, 1967. To date, three species from northern Siberia (Russia) have been described: R. gigantoides (Pavlow, 1914), R. obscurus (Nalnjaeva, in Sachs & Nalnjaeva 1970), and R. procerus (Nalnjaeva, in Sachs & Nalnjaeva 1970). In this study, we present evidence of a wider geographic distribution for R. gigantoides, i.e. from East Greenland on the west to the Omolon massif region of northeastern Russia on the east. At the end of the earliest Toarcian Dactylioceras tenuicostatum Zone, with the beginning of the Toarcian OAE, a significant extinction event affected the Passaloteuthididae and other Coleoidea in northwestern and Central Europe. While the first, but sporadic appearance of Megateuthididae occurred in the Pliensbachian, a major diversification of this megateuthidid fauna occurred from the Early Toarcian Hildoceras bifrons Zone onward both in and outside Europe. In the Arctic, this family first appeared not later than the beginning of the Early Toarcian Harpoceras falciferum Zone.